Photographic fine grain silver halide materials

ABSTRACT

A method of preparing a photographic fine-grain silver halide emulsion is described wherein precipitation of the silver halide occurs in the presence of a compound corresponding to the formula:   WHEREIN Z represents the atoms necessary to complete an imidazole, benzimidazole or naphthimidazole nucleus; Q is sulphur or selenium; R is hydrogen, C1-C4 alkyl or aryl, A is alkylene, which may be interrupted by hetero atoms, -S-alkylene which may be interrupted by hetero atoms, or arylene and X is alkyl, alkenyl or aryl or A and X together with Q represent the atoms necessary to complete a non-nitrogen containing heterocycle. By the presence of these compounds during precipitation of the silver halide homogeneous Lippmann-emulsions can be prepared with an average grain-size of less than 50 nm.

United States Patent [151 3,661,592 Philippaerts et al. 1 May 9, 1972 [54] PHOTOGRAPHIC FINE GRAIN SILVER ABSTRACT HALIDE MATERIALS Assignee: Gevaert-Agfa N.V., Mortsel, Belgium Filed: Oct. 2, 1970 Appl. No.: 77,694

[30] Foreign Application Priority Data Nov. 6, i969 Great Britain ..54,539/69 US. Cl ..96/94, 96/1 14.6 Int. Cl ..G03c 1/02 Field of Search ..96/94, I 14.7, 114.6

[56] References Cited UNITED STATES PATENTS 1 H1964 Wartburg ..96/45 6/1966 Johnson ..260/309.2

Primary Examiner-Norman G. Torchin Assistant Examiner-Judson R. Hightower Attorney-Brufsky, Staas, Breiner and Halsey A method of preparing a photographic fine-grain silver halide emulsion is described wherein precipitation of the silver halide occurs in the presence of a compound corresponding to the formula:

wherein Z represents the atoms necessary to complete an imidazole, benzimidazole or naphthimidazole nucleus; Q is sulphur or selenium; R is hydrogen, C -C alkyl or aryl. A is alkylene, which may be interrupted by hetero atoms. -S-alkylene which may be interrupted by hetero atoms. or arylene and X is alkyl, alkenyl or aryl or A and X together with Q represent the atoms necessary to complete a nonnitrogen containing heterocycle. By the presence of these compounds during precipitation of the silver halide homogeneous Lippmann-emulsions can be prepared with an average grain-size of less than 50 mm.

4 Claims, No Drawings PHOTOGRAPI-IIC FINE GRAIN SILVER HALIDE MATERIALS The present invention relates to the preparation of lightsensitive silver halide emulsions, more particularly to the preparation of fine-grain silver halide emulsions of the Lippmann type, to fine-grain silver halide emulsions prepared according to this method and to photographic elements having at least one layer of such a fine-grain silver halide emulsion.

Lippmann-emulsions, normally having an average grain-size of about 50-100 nm, are of particular importance for the preparation of photographic plates or films with high resolution, for use in microphotography and in astrophotography, for recording nucleo-physical phenomenons, for the preparation of masks in the production of microelectronic integrated circuits, for use in holography, etc.

Nowadays there is an increasing demand for photographic plates or films having Lippmann-emulsion layers, the average grain-size of which is less than 50 nm. These materials are of particular importance for reflection holograms where a high diffraction efficiency and a high signal to noise ratio are required.

Attempts to prepare Lippmann-emulsions with an average grain-size smaller than usual i.e. smaller than 50 nm by varying the working conditions during the precipitation of the silver halide have not been successful and therefore, it has been tried to use compounds restraining the growth of the silver halide crystals during precipitation.

It has now been found that silver halide emulsions with very fine grain can be prepared by effecting the precipitation of the silver halide in an aqueous hydrophilic colloid medium in the presence of compounds corresponding to the following general formula wherein Z stands for the atoms necessary to close an imldazole, benzoimidazole or naphthoimidazole nucleus which may be further substituted,

Q stands for sulfur or selenium,

R stands for hydrogen, alkyl comprising at most 4 C-atoms, or aryl,

A stands for alkylene for example methylene, ethylene, trimethylene, etc. including substituted alkylene and alkylene interrupted by one or more heteroatoms, S-alkylene including substituted S-alkylene and S-alkylene interrupted by one or more heteroatoms or arylene including substituted arylene, and

X stands for alkyl including substituted alkyl, alkenyl including substituted alkenyl or aryl including substituted aryl,

A and X together with Q represent the atoms necessary to complete a non-nitrogen containing heterocycle for example thiophene and tetrahydrothiophene.

The compounds corresponding to the above general formula contain two coordinating atoms for silver, a nitrogen atom of the imidazole heterocycle being one of the coordinating atoms and the Q-atom, i.e. sulfur or selenium being the other coordinating atom, and thus are bidentate ligands forming complexes with silver, thus restraining growth of the silver halide crystals so that very fine silver halide grains are formed.

Closely similar compounds differing from the compounds of the invention only in that the group Q-X is directly linked to the heterocycle, i.e. compounds wherein A is a chemical bond would be unsuitable because in this case the sulfur or selenium atom loses its coordinating action with regard to silver since when directly linked to the heterocycle the unshared electron pairs on the sulfur or selenium atom (Q) are interacting with the delocalized or spread 'rr-electrons of the strongly electronwithdrawing heterocycle i.e. they are held in common by the whole of the conjugate system. This is not the case with the compounds corresponding to the above formula since the intervening group A prevents interaction of the unshared electron pairs of the Q-atom with the ir-electrons of the nucleus i.e. conjugation does not extend as far as the Q-atom.

By the use of compounds corresponding to the above general formula during the precipitation step of the silver halide, homogeneous Lippmanmemulsions can be prepared with an average grain size markedly smaller than in the absence of said compounds so that emulsions are obtained practically without scattering.

The compounds or solution of the compounds of use according to the present invention are generally incorporated into the aqueous hydrophilic colloid composition, more particularly aqueous gelatin, into which the silver halide is precipitated. They can be used in amounts varying between very wide limits, preferably between 2 g and 20 g per mole of silver halide.

The ratio of hydrophilic colloid binder to silver halide in the fine-grain emulsions according to the present invention is preferably comprised between 0.2 and 6.0.

The hydrophilic colloid used as the vehicle for the silver halide may be any of the common hydrophilic colloids employed in photographic light-sensitive emulsions, for example gelatin, albumin, zein, casein, alginic acid, collodion, 'a cellulose derivative such as carboxymethyl cellulose, a synthetic hydrophilic colloid such as polyvinyl alcohol and poly-N-vinyl pyrrolidone, etc. gelatin being however preferred. If desired compatible mixtures of two or more colloids may be-employed for dispersing the silver halide.

Various silver salts may be used as the light-sensitive salt such as silver bromide, silver chloride or mixed silver halides such as silver chlorobromide, silver bromoiodide and silver chlorobromoiodide. Emulsions containing silver bromide or silver chloride or a mixture of silver chloride and silver bromide and such emulsions containing small amounts of silver iodide up to 8 percent are favored.

After precipitation of the silver halide grains in the presence of the compounds of use according to the present invention the emulsion is washed in order to remove the water-soluble salts whereupon the emulsions may be chemically as well as spectrally sensitized.

They may be spectrally sensitized by any of the known spectral sensitizers such as cyanines and merocyanines for photographic silver halide materials. They may be chemically sensitized by means of sulfur compounds for example allyl thiocyanate, allyl thiourea, sodium thiosulfate, etc. They may also be sensitized by means of reductors for instance tin compounds, imino-amino methane sulfinic acids and derivatives thereof, cadmium salts, and small amounts of noble metal compounds such as gold, platinum, palladium, iridium, ruthenium and rhodium. The emulsions according to the invention may also comprise compounds which sensitize the emulsion by development acceleration e.g. quaternary ammonium compounds and compounds of the polyoxyalkylene type.

Further, the emulsions may comprise antifoggants and stabilizers for example heterocyclic nitrogen-containing thioxocompounds such as benzothiazoline-2-thione and l-phenyl- 2-tetrazoline-5-thione, compounds of the hydroxytriazolopyrimidine type such as 5-methyl-7-hydroxy-striazolo[ 1,5-a] pyrimidine and mercury compounds.

Any of the hardening agents for hydrophilic colloids may be used in the emulsions according to the present invention for example formaldehyde, dialdehydes, diketones, halogen substituted aldehyde acids such as mucochloric acid and mucobromic acid, etc.

The emulsions may be coated on a wide variety of photographic emulsion supports. Typical supports include cellulose ester film, polyvinyl acetal film, polystyrene film, polyethylene terephthalate film and related films of resinous materials as well as paper and glass. v

The following example illustrates the present invention Under completely analogous working conditions other emulsions were prepared with the difference that the 10 percent aqueous solution of gelatin into which the silver bromide was precipitated now contained one of the compounds listed in the table. below in an amount of 8.5 g compound per mole of silver nitrate used.

The average silver bromide grain size was determined by turbimetry.

The results attained are listed in the table below and show that the compounds corresponding to the above general formula restrain growth of the silver halide grains.

Averag grain-silt.- Numbnr Compound added in mm.

None 67 C-CHzSCH2fi H 39 N HOaS- C(CH2)2SCH3 H 4 HOaS- L fi-CHr-S- HO3S- N N CH CH3 I l I C-CIlg-SCCII2-C-CII3 U s 0 all CilgHs (CHz)3s0H HOaS N l IIO3S- The compounds used in the above Example can be prepared as described in the following preparations. Preparation 1 :Compound 1 To a suspension of 83.2 g (0.5 mole) of 2-chloromethyl benzimidazole in 350 ml of ethanol, a solution of 93 g (0.5 mole) of the sodium salt of Z-mercapto-methyl-benzimidazole was added. The mixture was stirred for 4 hours, refluxed and then concentrated by evaporation. The residue was washed with water and recrystallized from a mixture of 250 ml of water and 750 ml of methanol. The product obtained was dried in vacuum at 80 C.

Yield: 37.5 g.

Preparation 2 Compound 2 12.7 g of 3,4-diaminobenzene sulfonic acid and 8 g of B- methyl-thiopropionic acid were refluxed for 12 hours in 100 ml of 6N hydrochloric acid. The solution was filtered over decolorizing carbon, the hydrochloric acid was evaporated and the residue was recrystallized from water.

Yield: 8 g.

Preparation 3 Compound 3 20.6 g of 3,4-diaminobenzenesulfonic acid and 21.5 g of (phenylseleno)acetic acid prepared according to J1. Chem.Soc. i928, 2293, were refluxed for 12 hours in 500 ml of 6N hydrochloric acid and 200 ml of dioxan. The solution was filtered over decolorizing carbon, the solvents removed by evaporation and the residue taken up in alkali. The solution was filtered and acidified whereupon the solid formed was filtered and recrystallized from water.

Yield 8 g.

Preparation 4 Compound 4 94 g of 3,4-diaminobenzenesulfonic acid and 84 g of (phenylthio)acetic acid were refluxed for 12 hours in 2.6 liters of 6N hydrochloric acid. The solution was filtered over decolorizing carbon, the hydrochloric acid was removed by evaporation and the residue recrystallized from methanol.

Yield: 69 g.

Preparation 5 Compound 5 To a solution of 8.2 g of 2mercaptomethylbenzimidazole and 2.7 g of sodium methylate in 100 ml of methanol were added 8.2 g of l,l,3trimethylpropanesultone whereupon the whole was refluxed for 2 hours. The solution was filtered over decolorizing carbon, the methanol was removed by evaporation and the residue was taken up in alkali. The solution formed was filtered and acidified. By crystallization from water 3 g were obtained.

Preparation 6 Compound 6 This compound was prepared as described in Ber. 90, 815 (1957).

Preparation 7 Compound 7 To a solution of 23.4 g (0.1 mole) of N-monoethyl-4-sulfoo-phenylene diamine in 200 ml of 5N hydrochloric acid, 13.4 g (0.1 mole) of methylmercapto-butyric acid were added. The mixture was refluxed for 12 hours and then concentrated by evaporation. The residue was dissolved in 5 N sodiumhydroxide,filtered and precipitated by addition of acetic acid. After filtration by suction the product was recrystallized from l50 ml of water.

Yield 20 g.

Preparation 8 Compound 8 To a solution of 54.8 g of the disodium salt of 2-mercapto-5 (6)-sulfobenzoimidazole in 250 ml of dimethylformamide a solution of 25 g of 2-chloroethylthioethane in 50 ml of. dimethylformamide was added slowly with stirring. The temperature was kept between 80 and 90 C for 3 hours. The

sodium chloride formed was filtered off and the dimethylformamide was removed by evaporation. The brown solid formed was taken up in alkali, filtered over decolorizing carbon and acidified. The precipitated product was recrystallized from water.

Yield 36 g.

We claim 1. Method of preparing a photographic fine-grain silver halide emulsion which comprises the step of precipitating the silver halide in an aqueous hydrophilic colloid medium in the presence of a compound corresponding to the following general formula wherein Z stands for the atoms necessary to close an imidazole, benzimidazole or naphthimidazole nucleus,

Q stands for sulfur or selenium,

R stands for hydrogen, alkyl comprising at most 4 C-atoms, or aryl,

A stands for an alkylene group, an alkylene group interrupted by one or more heteroatoms, an S-alkylene group, an S-alkylene group interrupted by one or more heteroatoms or an arylene group, and

X stands for an alkyl group, an alkenyl group or an aryl group,

A and X together with Q represent the atoms necessary to complete a non-nitrogen containing heterocycle.

2. Method according to claim 1, wherein said compound is present in the aqueous hydrophilic colloid medium into which the silver halide is precipitated in an amount sufficient to effectively restrain growth of the silver halide grains.

3. Method according to claim 1 wherein the emulsion is a silver bromide, silver chloride or a silver chlorobromide emulsion which may comprise a minor amount of silver iodide.

4. A photographic fine-grain silver halide emulsion prepared by precipitating the silver halide in an aqueous hydrophilic colloid medium in the presence of a compound corresponding to the formula wherein: Z stands for the atoms necessary to close an imidazole, benzimidazole or naphthimidazole nucleus, Q stands for sulfur or selenium R stands for hydrogen, alkyl comprising at most 4 C-atoms, or aryl, A stands for an alkylene group, an alkylene group interrupted by one or more heteroatoms, an S-alkylene group, an S-alkylene group interrupted by one or more heteroatoms or an arylene group, and X stands for an alkyl group, an alkenyl group or an aryl group,

or A and X together with 0 represent the atoms necessary to complete a non-nitrogen containing heterocycle. 

2. Method according to claim 1, wherein said compound is present in the aqueous hydrophilic colloid medium into which the silver halide is precipitated in an amount sufficient to effectively restrain growth of the silver halide grains.
 3. Method according to claim 1 wherein the emulsion is a silver bromide, silver chloride or a silver chlorobromide emulsion which may comprise a minor amount of silver iodide.
 4. A photographic fine-grain silver halide emulsion prepared by precipitating the silver halide in an aqueous hydrophilic colloid medium in the presence of a compound corresponding to the formula : 